what kind of fabric shops are you looking for? clothes or furniture?
There is DUMIT on calle del sol in the city (along with quite a few others on the same street). La Opera sells fabric for a decent price, but often lacks variety (on the second floor)
The is a DUMIT by plaza internacional as well with some more high-end fabrics
On San Luis, below Restauracion there is a fabric store with a nice selection and decent prices. In front is a store that sells curtain and furniture fabric.